An Irishman shot dead in Bolivia was linked to a gang of neo-fascist extremists with roots in the Yugoslav civil war. The body of Michael Dwyer arrived in Ireland on Thursday night and a post-mortem examination is due in the next two days.

Bolivian police claim that Dwyer, 24, from Tipperary, was killed during a 30-minute gun fight in the city of Santa Cruz. However, Dwyer and two other men were asleep when the shooting started around 4am on 16 April. The Irish government is demanding an international investigation into his death.

Dwyer died alongside Eduardo Rozsa Flores, an adventurer who held a Croatian passport, and Arpad Magyarosi, a Romanian of Hungarian ethnicity. Bolivian authorities claim the trio were hatching a plot to assassinate the country's left-wing President Evo Morales.

It is now understood that Dwyer's associates were members of a group responsible for racist murders and attacks on indigenous Bolivians.

Dwyer's family are seeking an inquiry into the circumstances surrounding his death. It appears that Dwyer was drawn to the group after becoming a Facebook "friend" of gang leader Rozsa Flores, who was openly antisemitic and is believed to have been backed by right-wing elements in the wealthy city of Santa Cruz.

Bolivia was once a haven for members of the Croatian Ustashe fascist government. They fled to South America after the second world war, fearing retribution for siding with the Nazis and committing war crimes. Their passage to countries such as Bolivia was organised by Croatian clergy operating out of the Vatican.

Rozsa Flores was of Hungarian-Bolivian background, and at the start of the conflict in former Yugoslavia he sided with the right-wing Catholic Croatian militia who were responsible for some of the worst atrocities at the start of the civil war. He led an armed group which attracted foreign right-wing elements and used the nickname "Franco" in honour of Spain's right-wing dictator.

Dwyer would not be the first Irishman to find himself mixed up with right-wing extremists with links to Croatian militias. During the civil wars of the 1990s, at least one Irish national from the prosperous Killiney area of south Dublin lost his legs after fighting with the ultra-right HOS Croatian militia in Bosnia.

Rozsa Flores, 49, had been a left-wing journalist but turned neo-Nazi and joined Croatian forces when the civil war broke out in former Yugoslavia. He was a suspect in the murder of British photographer Paul Jenks and of a Swiss journalist who are both believed to have uncovered information about atrocities committed by Rozsa Flores and his militia.

He was part of the notorious "Zenga" unit of the Croatian militia, which is blamed for ethnic cleansing in former Yugoslavia in 1991. Since then, he had continued to recruit and organise right-wing extremists. His antisemitism is believed to have led him to convert to Islam, despite being homosexual.

It is thought that Dwyer fell in with the gang after meeting eastern European supporters of Rozsa Flores working as security staff in Ireland. Dwyer, although described by friends as a pleasant young man, had a self-confessed obsession with guns and martial arts.

Morales said last week that he had no objection to an international inquiry into the killings. Bolivian government officials said that Rozsa Flores had arrived in the country last October, crossing the border from Brazil. It emerged last week that, before he left Hungary, Rozsa Flores recorded an interview with a journalist which he said was only to be released in the event of his death. He said there was a "legal background" to his mission, which was to "drive away the president" and organise "resistance".

The Hungarian government has also been in touch with the Bolivian authorities.